Abstract: <FONT face=Verdana>Optimum conditions of preparing nano-sized titanium dioxide (TiO2) powder by atmospheric hydrolysis method were studied,in which the intermediate product titanyl sulfate (TiOSO4) from industrial titanium dioxide production with sulfuric acid process and industrial urea were used as raw materials.Major influencing factors,such as mass concentrations of titanyl sulfate and urea,as well as amount-of-substance ratio of titanyl sulfate to urea in production process of nano-sized TiO2 were investigated.According to experimental parameters,optimum program for preparation of nano-sized TiO2 was obtained.Namely,amount-of-substance ratio of TiOSO4 to CO(NH2)2 was 1∶2,mass concentrations of TiOSO4 and CO(NH2)2were 40 g/L and 50 g/L,respectively;adding a certain amount of surfactant into the reaction system;reaction temperature was 85 ℃±5 ℃,reaction time was 2 h under high-speed stirring,and maintaining pH at 2.After reaction,the product was washed with deionized water,and then washed again with ethanol.Finally,nano-sized TiO2 was obtained after the product was dried at 85 ℃ for 2～3 h and calcined at 700 ℃ for 2 h.Prepared TiO2 was anatase&nbsp; with particle size of 7～13 nm. </FONT>